1. Field of the Invention
The present invention relates to a signal processor or integrated circuit for use in an electronic compass, and more particularly to a signal processor for use in an electronic compass, which can maintain levels of signals to be inputted into an analog/digital (AD) converter through offset and gain control operations within a reference voltage range by controlling an offset voltage generated while processing analog signals and automatically controlling a signal amplification gain, be applicable to performing a tilt compensation operation for a sensor, improve sensor performance by carrying out a gain control operation for signals from a geomagnetic compass sensor and minimize an error when calculating an azimuth angle.
2. Description of the Related Art
Conventionally, an azimuth angle used for identifying a ship route or position is of the utmost importance to ship navigation. The azimuth angle has been measured using a magnet pointing to the magnetic north for the past several hundred years. Representative devices for measuring the azimuth angle include a magnetic compass and a gyrocompass. The magnetic compass is a device for measuring the azimuth angle using properties of the earth's magnetic field. The principle of the magnetic compass is simple, but the precision of the magnetic compass may be degraded due to the distortion of the earth's magnetic field. In particular, internal and external functions associated with small-sized excursion ships or small-sized fishing boats have been recently modernized. However, there are problems in that the functions of the ships or boats are still insufficient and other electronic devices contained in the ships or boats cannot use stem angle information obtained from the magnetic compass.
Furthermore, as another azimuth measuring device, the gyrocompass is used. The precision of the gyrocompass is remarkably higher than that of the magnetic compass, but there are problems in that the gyrocompass is expensive and inappropriate to small-sized fishing boats and yachts that must frequently come in to and go out of a port or harbor. To address the above-described problems, an electro magnetic compass was developed. This electro magnetic compass was commercialized and used in Europe and America a long time ago.
The electro magnetic compass (hereinafter, referred to as an “electronic compass”) basically includes a sensor for detecting a magnetic field azimuth and converting the detected azimuth into an electric signal, a signal processor for calculating an azimuth angle on the basis of the signal from the sensor and a display unit for displaying the azimuth angle. The sensor for detecting the magnetic field azimuth uses a flux valve, and the flux valve uses a set of X-Y orthogonal coils called a flux gate. The signal processor calculates the azimuth angle. The display unit displays the calculated azimuth angle.
The conventional signal processor for use in the electronic compass is shown in FIG. 1.
Referring to FIG. 1, the conventional signal processor for use in the electronic compass includes a geomagnetic compass sensor 11 for detecting voltages of sine or cosine wave signals induced by a drive signal according to a rotating angle of a flux-gate sensor; an analog signal processor 12 for filtering and amplifying x-axis and y-axis signals Sx and Sy from the geomagnetic compass sensor 11; an analog/digital (AD) converter 13 for converting voltages Vadcx and Vadcy from the AD converter 13 into a set of digital signals; and a digital signal processor 14 for detecting an azimuth angle from the set of digital signals outputted by the AD converter 13.
FIG. 2 is a waveform diagram illustrating input signals inputted into the AD converter 13 shown in FIG. 1.
Referring to FIG. 2, the two voltages Vadcx and Vadcy inputted into the AD converter 13 are ideally within a reference voltage range (e.g., a range of ±500 mV). The digital signal processor 14 produces an azimuth angle θ using the two voltages Vadcx and Vadcy according to the following Equation 1.                     θ        =                              tan                          -              1                                ⁡                      (                          Vadcy              Vadcx                        )                                              Equation        ⁢                                   ⁢        1            
However, where a sensor leans to one side as it is put on an uneven plane, there is a problem in that the amplitude of the voltage Vadc (Vadcx or Vadcy) inputted into the AD converter 13 is out of the reference voltage range. Also where an offset voltage occurs within the analog signal processor, there is the problem in that the amplitude of the voltage Vadc (Vadcx or Vadcy) inputted into the AD converter 13 is out of the reference voltage range.
In the conventional method, signal amplitude cannot be appropriately adjusted since the analog signal processor is based on a fixed amplification gain. In relation to the conventional method, the offset voltage occurs within the analog signal processor and also when an intensity of the earth's magnetic field varies with the environment in which it is used. When the input signal for the AD converter deviates from an allowable input range, an azimuth-angle calculation error increases.
Where an offset associated with at least one voltage of the two voltages occurs or one voltage has an amplitude higher than the other voltage, related problems occur, and will be described with reference to FIGS. 3(a), 3(b) and 3(c) and FIGS. 4(a), 4(b) and 4(c).
FIGS. 3(a), 3(b) and 3(c) are waveform diagrams illustrating an offset occurrence, offset calibration and azimuth-angle error occurrence associated with input signals.
Where an offset associated with the input signals occurs as shown in FIG. 3(a), the offset calibration for the input signals is carried out as shown in FIG. 3(b). In this case, it can be found that an azimuth-angle error occurs as shown in FIG. 3(c).
In other words, where an offset voltage occurs within the analog signal processor, a voltage Vadc deviating from the allowable input range for the AD converter can be outputted as shown in FIG. 3(a). At this time, the digital signal processor carries out a calibration operation for the voltage Vadc deviating from the allowable input range so that the same signal amplitudes can be maintained for the azimuth-angle calculation. As shown in FIG. 3(b), the voltage Vadc deviating from the allowable input range for the AD converter is cancelled out. When the azimuth angle is calculated by the above Equation 1, the azimuth-angle error occurs as shown in FIG. 3(c). This error is increased as the voltage Vadc deviating from the allowable input range for the AD converter is increased.
FIGS. 4(a), 4(b) and 4(c) are waveform diagrams illustrating gain error occurrence, error correction and azimuth-angle error occurrence associated with the input signals.
Where amplitude of the input signal is very large or very small as shown in FIG. 4(a), the amplitude is corrected as shown in FIG. 4(b). In this case, it can be found that an azimuth-angle error occurs as shown in FIG. 4(c).
Where the amplitude of a signal generated from the sensor is very large or an amplification gain of the analog signal processor is set to be very large in the conventional signal processor, the voltage Vadc as shown in FIG. 4(a) can be outputted. In this case, although the offset voltage does not occur, an error occurs as shown in FIG. 4(c) when the signal amplitude deviates from the allowable input range for the AD converter as shown in FIG. 4(a).
A system offset cannot be completely cancelled out without a separate control operation in the conventional method. Since levels of signals from the sensor are not constant, the azimuth-angle error causes the above-described problems.